Electrolytic switches, or "bubble" switches as they are commonly known in the art, typically include a glass chamber partially filled with an electrically conductive medium or electrolyte, so that a bubble is disposed at the top of the chamber for engagement with one or more electrodes according to the orientation of the chamber. Tilting the chamber causes the bubble to shift and exposes more or less of the surface of the electrodes to the electrolyte. Switches of the type described are used in inertial instruments to control the deviation of the instruments from true vertical. In a typical implementation a plurality of electrodes are spaced about the switch chamber and the instruments are controlled by an arrangement responsive to the differential current flow through the respective electrodes as the bubble shifts in response to tilting of the instrument.
A typical prior art electrolytic switch is described in U.S. Pat. No. 2,713,727 issued to Louis Balsam on July 26, 1955. A typical switch electrolyte is described in U.S. Pat. No. 2,387,313 issued to Elwood Wilson on Oct. 23, 1945. Other electrolytic switches and implementations thereof of which the applicant is aware are described in U.S. Pat. No. 2,720,569 issued to John F. Schoeppel, et al on Oct. 11, 1955; U.S. Pat. No. 2,830,159 issued to Stuart Varner on Apr. 8, 1958; U.S. Pat. No. 2,977,559 issued to Andrew Rosenberg, et al on Mar. 28, 1961; U.S. Pat. No. 4,312,131 issued to Peter Scriffignana on Jan. 26, 1982; U.S. Pat. No. 4,536,967 issued to George Beitzer on Aug. 27, 1985; and U.S. Pat. No. 4,583,296 issued to Robert Dell'Acqua on Apr. 22, 1986.
In many current applications it has become necessary to improve the ultimate performance of the prior art switches, particularly when the switches are used in the aerospace and land navigation fields. The improved performance is required for: increased null stability, scale factor and linearity; minimization of a secondary time constant; and improved performance over an ambient temperature range, particularly at lower temperatures.
It has been found that electrostatic charges on the exterior of the switch chamber, while having a relatively small effect on electrolytic switch characteristics under most circumstances, do tend to degrade the performance of the switches when performance requirements are extended to the arc-second of angle realm. The prior art has not considered these electrostatic charges and their effect on switch performance.
This invention minimizes the effect of the aforenoted electrostatic charges by providing a ground plane on the exterior of the switch chamber for "bleeding off" said charges.